Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
The typical image sensor operates as follows. Image light from an external scene is incident on the image sensor. The image sensor includes a plurality of photosensitive elements such that each photosensitive element absorbs a portion of incident image light. Photosensitive elements included in the image sensor, such as photodiodes, each generate image charge upon absorption of the image light. The amount of image charge generated is proportional to the intensity of the image light. The generated image charge may be used to produce an image representing the external scene.
Phase detection in image sensors may be achieved by separating light incident on an image sensor into pairs of images and comparing the two images. The two images may be analyzed for similar patterns (peaks and valleys in light intensity) and separation error is calculated. This allows the image sensor determine if the object is in a front focus or back focus position. Knowing the focus of the images allows the camera to autofocus optically, digitally, or the like. Despite advances in this field, there is still appreciable room for device architecture improvement.